It is well known that it can be difficult to start an internal combustion engine from a cold condition, particularly during cold weather conditions. When an engine is out of service, the engine lubricating oil will achieve a temperature consistent with the ambient air temperature, and it will become highly viscous. Upon starting the engine from the cold condition, the lubricating oil will gradually warm to its normal operating temperature. However, during the warm-up period, the operation of the lubricating system is degraded due to the high viscosity of the oil. Cold starting of an internal combustion engine is made more difficult due to the increased friction caused by the high oil viscosity, and engine parts may experience accelerated wear rates during the warm-up period due to the degraded lubricating system performance.
Self-propelled vehicles commonly utilize an internal combustion engine as a prime mover. The assignee of the present invention is a supplier of locomotives powered by turbo-charged diesel engines, such as the General Electric model GE7FDL16 diesel engine. Such engines are subject to the disadvantages discussed above during cold starting conditions. Furthermore, the operating instructions for a locomotive may include limitations on the engine throttle settings prior to the engine achieving full operating temperature. In cold weather conditions, there may be a delay of more than one hour after starting the locomotive engine from cold conditions until the engine is capable of operating at full throttle. U.S. Pat. No. 4,592,323 issued to Vest on Jun. 3, 1986, and assigned to the assignee of the present invention, discloses a system for limiting the maximum speed of the diesel engine of a locomotive when the lubricating oil is relatively cool and hence highly viscous. The Vest patent describes the design and operation of a diesel locomotive engine system in some detail and is incorporated by reference herein. For some applications, such as when operating in a switch yard, a locomotive is used for only short periods followed by periods of inactivity. In order to avoid delays in the availability of such engines, particularly in cold weather conditions, it is common for the engine of the locomotive to be placed in the idle position during periods of inactivity. Although this approach is effective in maintaining the engine at operating temperature, it also results In the wasting of fuel during the idling periods. Alternatively, the engine may be shut down between periods of operation in order to conserve fuel, however, this increases the risk the temperature of the lubricating oil will drop below the desired operating level.
FIG. 1 illustrates the lubricating oil system of a prior art diesel locomotive engine 10. An oil pump 12 draws oil from the engine 10 and delivers it to an oil cooler 14. The oil cooler 14 functions to transfer heat from the engine oil to a cooling water supply (not shown). The oil is then pumped through a filter 16 and returned to engine 10. For many applications, such as the GE7FDL16 diesel engine, the temperature of the oil is measured at a point in the lubricating oil system that is remote from the engine 10. As illustrated in FIG. 1, it is common for the temperature of the oil to be measured by a temperature sensor 18 located downstream of pump 12 near the inlet of cooler 14. Such a location is convenient for the design of the lubricating oil system, and it provides an accurate measurement of the lubricating oil temperature during the operation of the engine. However, during periods of engine shutdown, the oil becomes stagnate within the lubricating oil system and/or drains completely out of the filter 16 and cooler 14 and returns to the engine 10. Therefore, during engine shutdown conditions, temperature measuring device 18 is ineffective for providing an indication of the lubricating oil temperature within engine 10. Therefore, the operator of the locomotive will have no reliable indication of the actual lubricating oil temperature within engine 10 and will be unable to predict whether the operation of the engine 10 will be delayed upon startup due to lubricating oil temperature limitations. As a result, in order to assure that the locomotive will always be available for full power service, it is common practice to allow the engine to operate at idle conditions during periods of inactivity.